1. Field of the Invention
The present invention relates to a method for evaluating a lithography system for producing devices such as semiconductor elements, liquid crystal display elements, plasma display elements, and thin film magnetic heads. In particular, the present invention is preferably applied to a lithography system provided with a resist coater, an exposure apparatus, and a developing apparatus (developer).
2. Description of the Related Art
In order to respond to the improvement in degree of integration and degree of fineness of the semiconductor device, it is demanded to enhance the image formation characteristics such as the resolving power and the transfer faithfulness for the exposure apparatus to be used for the lithography step (representatively comprising the application step, the exposure step, and the resist development step) in order to produce the semiconductor device. In order to enhance the image formation characteristics as described above, for example, the following means are adopted for the exposure apparatus. That is, the wavelength of the exposure light beam as the exposure beam is shortened, the numerical aperture of the projection optical system is increased, and the new illumination system such as the modified illumination is developed.
In order to evaluate how the image formation characteristic is actually improved when the exposure condition (for example, the exposure wavelength, the numerical aperture of the projection optical system, and the illumination system) is changed, for example, the following procedure has been hitherto adopted. That is, an image of a line-and-space pattern having a line width approximate to the resolution limit is projected onto a wafer applied with photoresist by the aid of a projection optical system. For example, the line width of the resist pattern, which is obtained after development of the wafer, is measured with the scanning electron microscopy (SEM). An obtained result of the measurement is compared with the data having been measured and stored. However, in the case of this method, the following inconvenience arises. That is, the equipment for performing the evaluation is expensive, because the scanning electron microscope is required in addition to the exposure apparatus. Further, the operation to perform the evaluation is complicated, and the period of time required for the evaluation is prolonged.
In view of the above, in order to conveniently evaluate the image formation characteristic of the exposure apparatus, the following evaluation method has been suggested, as disclosed in Japanese Patent No. 2530080. That is, a plurality of resistor patterns are formed on a semiconductor substrate by using an exposure apparatus and an etching apparatus. The size of the resistor pattern is indirectly determined by measuring resistance values of the resistor patterns.
As described above, the method for performing the evaluation relatively conveniently has been hitherto suggested for the image formation characteristic of the exposure apparatus alone. However, the final shape of the circuit pattern of the semiconductor device is affected not only by the image formation characteristic of the exposure apparatus but also, for example, by the uneven application caused when the photoresist is applied onto the wafer with a resist coater and the uneven development caused when the wafer (photoresist) is developed with a developing apparatus. Therefore, it is not easy to evaluate the image formation characteristic of the exposure apparatus alone after the exposure apparatus is once incorporated into the device-producing line including, for example, the resist coater, the developing apparatus, the baking apparatus, and the cooling apparatus.
On the other hand, in order to respond to further advance of integration of the semiconductor device, it is necessary to improve the accuracy of device production as brought about by the entire lithography system by optimizing the performance of the individual apparatuses including, for example, the exposure apparatus, the resist coater, and the developing apparatus which are included in the lithography system.
The present invention has been achieved from the viewpoint as described above, a first object of which is to provide an evaluating method for effectively evaluating the performance of individual apparatuses incorporated into a lithography system. A second object of the present invention is to provide a method for evaluating and/or adjusting a lithography system in order to improve the device-producing accuracy of a lithography system. A third object of the present invention is to provide a lithography system which makes it possible to effectively evaluate the performance of individual apparatuses incorporated into the lithography system.
Further, a fourth object of the present invention is to provide an adjusting method which makes it possible to easily adjust characteristics of a substrate-processing apparatus for constructing a lithography system together with an exposure apparatus. Still another object of the present invention is to provide an exposure apparatus which makes it possible to carry out the evaluating method as described above.
A first evaluating method for a lithography system according to the present invention lies in an evaluating method for a lithography process comprising an application step of applying a photosensitive material, an exposure step, and a development step in order to form a predetermined development pattern on a substrate applied with the photosensitive material; the evaluating method comprising exposing the substrate (W1 to W4) applied with the photosensitive material with a light beam via an evaluating pattern (36A to 36D, 48, 49, 62A to 62F); developing the exposed substrate to form a development pattern; observing a state of the formed development pattern including, for example, a thickness, a line width, a length, and a position; and determining, from a result of the observation, at least one factor of an application factor inherent in the application step, an exposure factor inherent in the exposure step, and a development factor inherent in the development step which affect the development pattern respectively, independently from the other factors.
According to the present invention as described above, the concave/convex pattern of the photosensitive material is formed on the substrate by actually exposing the substrate applied with the photosensitive material with the light beam via the predetermined evaluating pattern, and developing the substrate (photosensitive material) after the exposure. In this procedure, for example, the field for the substrate during the exposure is set to a predetermined narrow area so that the factor (for example, the image formation characteristic), which affects the development pattern in the exposure step (exposure apparatus), is made to be approximately constant. In this situation, the development pattern of the photosensitive material is formed, which undergoes the change of the factor which affects the development pattern in the application step (applying apparatus) and the factor which affects the development pattern in the development step (developing apparatus). Accordingly, for example, the thickness or the distribution of the line width of the state of the pattern is measured. Thus, the application factor (for example, uneven application) or the development factor (for example, uneven development) can be evaluated respectively. Further, the development pattern of the photosensitive material, which undergoes the change of the exposure factor, is formed by setting the field during the exposure for the substrate to be, for example, an area which is wide in approximately the same degree as that when a device pattern is actually subjected to the exposure, and performing the exposure for the evaluating pattern at the periphery of the field. In this case, in order to mitigate the influence of the change of the application factor and the development factor, for example, the characteristic of the exposure step (exposure factor) can be independently evaluated by averaging measured values at a plurality of positions on the substrate. In this procedure, the state of the pattern of the photosensitive material can be measured, for example, by using an alignment sensor provided for the exposure apparatus. Therefore, the evaluation can be performed easily at low cost. In order to execute the evaluation as described above, the evaluating pattern may include inherent patterns for determining the application factor, the development factor, and the exposure factor respectively.
A second evaluating method for a lithography system according to the present invention lies in a method for evaluating a lithography system comprising an applying apparatus (54) for applying a photosensitive material to a substrate, an exposure apparatus (50) for exposing the substrate applied with the photosensitive material, and a developing apparatus (59) for developing the photosensitive material; the method comprising a first step (steps 101, 120, 128) of applying the photosensitive material onto the substrate by using the applying apparatus; a second step (steps 105, 123, 131) of exposing the substrate applied with the photosensitive material with a light beam via an evaluating pattern (36A to 36C, 48, 49, 62A to 62F) by the aid of the exposure apparatus; a third step (steps 106, 124, 132) of developing the photosensitive material on the substrate by using the developing apparatus; a fourth step (steps 107, 110, 125, 133) of measuring a development pattern of the photosensitive material on the substrate having been subjected to the development; and a fifth step (steps 108, 111, 126, 134) of evaluating one characteristic of a characteristic of the applying apparatus, a characteristic of the exposure apparatus, and a characteristic of the development apparatus which affect the development pattern respectively, independently from the other characteristics, on the basis of a result of the measurement in the fourth step.
Also in the second evaluating method for the lithography system, the predetermined characteristic of arbitrary one of the applying apparatus, the exposure apparatus, and the developing apparatus can be easily evaluated independently from the characteristics of the other apparatuses, in the same manner as in the first evaluating method for the lithography system.
In this method, on condition that the exposure apparatus comprises a projection system (PL) for projecting an image of a mask pattern onto the substrate; an image of the evaluating pattern may be projected onto a plurality of comparted areas (SA) on the substrate through a predetermined narrow area (35A) in an effective field of the projection system in the second step; and the characteristic of any one of the applying apparatus and the developing apparatus may be evaluated in the fifth step.
Alternatively, an image of the evaluating pattern may be projected onto a plurality of comparted areas (SB) on the substrate through a predetermined wide area (35) in an effective field of the projection system in the second step; and any characteristic of the projection system (for example, the image formation characteristic) of the exposure apparatus may be evaluated in the fifth step.
Further, when the exposure apparatus is a scanning exposure type exposure apparatus for exposing the substrate by synchronously moving a mask and the substrate; then the image of the evaluating pattern may be projected onto the plurality of comparted areas (SC) on the substrate in accordance with a scanning exposure manner in the second step; and a dynamic control characteristic of the exposure apparatus may be evaluated in the fifth step.
The second evaluating method for the lithography system may further comprise a sixth step of measuring the dispersion of the length in the measuring direction of the development pattern of the photosensitive material formed in the plurality of comparted areas on the substrate; and a seventh step of evaluating uneven development of the developing apparatus. The evaluating method may further comprise an eighth step of applying the photosensitive material onto another substrate by using the applying apparatus; a ninth step of exposing the photosensitive material on the substrate applied with the photosensitive material by projecting an image of a pattern different from the evaluating pattern onto the plurality of comparted areas on the substrate through a predetermined wide area in the effective field of the projection system; a tenth step of developing the photosensitive material exposed in the ninth step; and an eleventh step of evaluating any characteristic of the projection system of the exposure apparatus by measuring a development pattern of the photosensitive material developed in the tenth step. The evaluating method may further comprise adjusting the projection system in accordance with the evaluated characteristic of the projection system. When the exposure apparatus is a scanning exposure type exposure apparatus for exposing the substrate by synchronously moving a mask and the substrate; then the evaluating method may further comprise a twelfth step of applying the photosensitive material to a test substrate by using the applying apparatus; a thirteenth step of projecting an image of an evaluating mask onto the plurality of comparted areas on the substrate in accordance with a scanning exposure manner to expose the photosensitive material; a fourteenth step of developing the photosensitive material exposed in the thirteenth step; and a fifteenth step of observing and evaluating a dynamic control characteristic of the exposure apparatus.
A third evaluating method for a lithography system according to the present invention lies in an evaluating method for a lithography system comprising an exposure apparatus (50) for exposing a substrate (W) applied with a photosensitive material, and a substrate-processing apparatus (51) for processing the substrate during at least one process to be performed before or after the exposure of the photosensitive material; the evaluating method comprising transferring an evaluating pattern onto the photosensitive material by using the lithography system to form a transferred image; measuring a state of the transferred image; and independently evaluating a characteristic of the exposure apparatus and a characteristic of the substrate-processing apparatus on the basis of a result of the measurement. According to this evaluating method, the characteristic can be evaluated with ease by measuring the state (for example, latent image) of the photosensitive material after the transfer.
In the third evaluating method, a size of an area of illumination of the evaluating pattern may be adjusted depending on the characteristic to be determined when the substrate is exposed with the evaluating pattern in order to independently determine the characteristic of the exposure apparatus and the characteristic of the substrate-processing apparatus. The evaluating pattern may include patterns to determine the characteristic of the exposure apparatus and the characteristic of the substrate-processing apparatus respectively, and a development pattern of the pattern corresponding to the characteristic to be independently determined may be observed. The substrate-processing apparatus may include an applying apparatus for applying the photosensitive material onto the substrate, and a developing apparatus for developing the photosensitive material formed with the transferred image.
According to still another aspect of the present invention, there is provided an adjusting method for a substrate-processing apparatus (51) which constitutes a lithography system together with an exposure apparatus (50) for exposing a substrate (W) applied with a photosensitive material and which treats the substrate during at least one process to be performed before or after the exposure of the photosensitive material; the adjusting method comprising transferring an evaluating pattern onto the photosensitive material on the substrate by using the lithography system to form a transferred image; measuring a state of the transferred image; and detecting a characteristic of the substrate-processing apparatus independently from a characteristic of the exposure apparatus on the basis of a result of the measurement. According to this adjusting method, the state (for example, resist pattern) of the photosensitive material after the transfer is detected, and thus the characteristic of the substrate-processing apparatus can be correctly evaluated on the basis of the result of the detection. The substrate-processing apparatus may include an applying apparatus for applying the photosensitive material onto the substrate, and a developing apparatus for developing the photosensitive material formed with the transferred image. The adjusting method may further comprise adjusting the substrate-processing apparatus when the detected characteristic does not satisfy a predetermined value.
A lithography system according to the present invention lies in a lithography system for forming a predetermined development pattern on a substrate applied with a photosensitive material; the lithography system comprising an applying apparatus (54) which applies the photosensitive material to the substrate; an exposure apparatus (50) which exposes the substrate applied with the photosensitive material; a developing apparatus (59) which develops the exposed photosensitive material; a control system (22) which controls the exposure apparatus so that the substrate, to which the photosensitive material has been applied by the applying apparatus, is exposed with a light beam via a predetermined evaluating pattern by the aid of the exposure apparatus; a sensor (23, 24) which measures a state of a development pattern of the photosensitive material obtained by developing the substrate exposed by the exposure apparatus by using the developing apparatus; and a judging system (27) which judges one characteristic of a characteristic of the applying apparatus, a characteristic of the exposure apparatus, and a characteristic of the developing apparatus which affect the development pattern respectively, independently from the other characteristics, on the basis of measurement information obtained by the sensor. According to this lithography system, the characteristics of the individual apparatuses for constructing the system can be measured independently, in which the maintenance can be easily performed, and it is possible to form a device pattern with a higher degree of accuracy. The evaluating method of the present invention can be carried out by using the lithography system.
The sensor may measure at least one of uneven application of the photosensitive material, uneven development, and an image formation characteristic of the exposure apparatus. The exposure apparatus may include a projection system which projects an image of the evaluating pattern onto the substrate and a field diaphragm which restricts an illumination field for the evaluating pattern illuminated by the projection system, and the control system may control the field diaphragm depending on the characteristic to be judged. A sensor provided for the exposure apparatus may be used as the sensor described above. Accordingly, the characteristics of the applying apparatus and the developing apparatus can be evaluated within the system without introducing any new sensor into the system. It is enough that the developed pattern is returned to the exposure apparatus again along with the production line of the system, for example, by using a transport system for transporting the substrate.
According to still another aspect of the present invention, there is provided an exposure apparatus for exposing a substrate (W) applied with a photosensitive material with a light beam via a mask (R); the exposure apparatus comprising an illumination system (1 to 18) which illuminates the mask; a substrate stage which positions the substrate; a variable field diaphragm (14B) which changes a size of an illumination area illuminated by the illumination system; a first sensor (24) which measures a physical quantity corresponding to a shape of a pattern of the photosensitive material after development of the substrate on the substrate stage; a second sensor (23) which measures a position of the pattern of the photosensitive material after the development of the substrate on the substrate stage; and a judging system (27) which evaluates a state of the photosensitive material on the substrate by using results of the detection performed by the first sensor and the second sensor. The exposure apparatus of the present invention can evaluate the characteristics of the applying apparatus and the developing apparatus. Therefore, when the exposure apparatus is incorporated into the lithography system, then it is easy to perform the maintenance for the system, and the performance of the system can be maximally extracted to further improve the accuracy of the development pattern of the device. The evaluating method of the present invention can be carried out by using the exposure apparatus.
The exposure apparatus of the present invention may further comprise a projection system which projects an illumination light beam from the illumination system onto the substrate. The judging system may evaluate an image formation characteristic of the projection system by using at least one of the first sensor and the second sensor. The physical quantity may be a thickness of the photosensitive material, and the state of the photosensitive material may include uneven application of the photosensitive material and uneven development. The exposure apparatus may further comprise a control system which controls the variable field diaphragm, wherein the control system may make control such that the variable field diaphragm is narrowed when the state of the photosensitive material on the substrate is evaluated as compared with when the image formation characteristic of the projection system is observed. The second sensor provided for the exposure apparatus may be used not only to measure the position of the pattern of the photosensitive material after the development, but also to execute alignment for the substrate with respect to the illumination light beam from the projection system.
According to still another aspect of the present invention, there is provided a method for producing a device based on the use of a lithography system; comprising a first step of applying a photosensitive material onto a substrate by using the applying apparatus as defined above; a second step of exposing the substrate applied with the photosensitive material with a light beam via an evaluating pattern by using the exposure apparatus as defined above; a third step of developing the photosensitive material on the substrate by using the developing apparatus as defined above; a fourth step of measuring a development pattern of the developed photosensitive material on the substrate; a fifth step of evaluating one characteristic of a characteristic of the applying apparatus, a characteristic of the exposure apparatus, and a characteristic of the developing apparatus which affect the development pattern respectively, independently from the other characteristics, on the basis of a result of the measurement performed in the fourth step; a sixth step of adjusting the apparatus having the evaluated characteristic in accordance with the evaluated characteristic; and a seventh step of executing the first to third steps by using a pattern for forming the device in place of the evaluating pattern after the adjustment performed in the sixth step to obtain the substrate on which a development pattern for forming the device is formed. According to the method for producing the device described above, it is possible to produce the highly accurate device with a high throughput, because the characteristics of the individual apparatuses which constitute the system are independently evaluated and adjusted in a well-suited manner.
According to still another aspect of the present invention, there is provided a measuring method for measuring an application state of a photosensitive material on a substrate to be exposed by using an exposure apparatus provided with an illumination system for illuminating the substrate applied with the photosensitive material and a detector for detecting a returning light beam from the illuminated substrate; the measuring method comprising exposing the substrate applied with the photosensitive material with a light beam via an evaluating mark; and observing a state of an exposed pattern of the evaluating mark subjected to the exposure by using the illumination system and the detector to determine the application state of the photosensitive material. According to this method, the application state of the photosensitive material can be inspected with ease by using the exposure apparatus. Therefore, the exposure apparatus can be used more effectively in the lithography process or in the lithography system. In this measuring method, a latent image, which is formed by exposure with the evaluating mark, may be observed. Alternatively, a diffracted light beam from the substrate may be observed by using a substrate on which a diffraction grating-shaped evaluating mark is formed. Further alternatively, the exposed evaluating mark may be developed to observe the development pattern. As for the detector described above, a detector, which is used to execute alignment for an exposure position of the substrate when the substrate is exposed, may be used. Further, a light beam from a light source possessed by the exposure apparatus may be used when the substrate is exposed with the light beam via the evaluating mark.
According to still another aspect of the present invention, there is provided a measuring method for measuring a development state of a photosensitive material on a substrate to be exposed by using an exposure apparatus provided with an illumination system for illuminating the substrate applied with the photosensitive material and a detector for detecting a returning light beam from the illuminated substrate; the measuring method comprising exposing the substrate applied with the photosensitive material with a light beam via an evaluating mark; developing the exposed substrate; and observing a development pattern of the evaluating mark subjected to the development by using the illumination system and the detector to determine the development state of the photosensitive material. According to this method, the development state of the photosensitive material can be inspected with ease by using the exposure apparatus. Therefore, the exposure apparatus can be used more effectively in the lithography process or in the lithography system.